Pipette tips are commonly used to transfer and dispense liquids, such as in scientific or medical testing. A typical pipette tip is made of plastic and formed with a substantially conical head and a frustoconical body. The head forms an opening at its proximal end while the body forms a smaller opening at its distal end. The pipette tip head has a larger outer diameter than the pipette tip body, and forms an annular lower edge at the junction of the head to the body. In use, the head of the pipette tip is typically force fit onto the shaft of another device, a pipettor, and held in place by friction. The pipettor is then operated to draw liquid into and expel liquid from the pipette tip through the distal opening in the tip body.
In most applications, pipette tips are used in large quantities, making individual handling of the pipette tips highly inconvenient. Consequently, a number of devices have been developed which manipulate numerous pipette tips at once for pickup or delivery of fluid. Typically, the pipette tip heads are inserted into a number of shafts on the device, with the positioning of the pipette tips and shafts chosen to be compatible with standard multi-well plates. The device positions the pipette tips into the wells of the plate, and liquid is drawn from the wells into the pipette tips, or liquid is expelled from the pipette tips into the wells. For compatibility between devices and plates, an industry standard has been developed for the spacing between the wells of the plates and for the spacing between the pipette tips when the pipette tips are mounted on the devices. Pipette tips are normally sold packaged in flats or racks which hold the tips in this desired spacing.
Those standard pipette tip racks and flats typically have a rectangular upper surface which defines an 8.times.12 array of 96 apertures, with approximately 9 millimeters separating the centers of each two adjacent apertures. Each aperture has a diameter larger than the outer diameter of the pipette tip body but smaller than the diameter of the annular lower edge of the pipette tip head. To store a pipette tip in the rack or flat, the body of the pipette tip is inserted into one of the apertures, and the annular lower edge of the pipette tip engages the upper surface of the rack or flat. The pipette tip then rests within the aperture with the head of the tip extending above the upper surface of the rack or flat and the body of the tip extending below the upper surface.
The industry has developed two primary methods for transporting pipette tips. In the first method, pipette tips are transported using a device which engages a rack or flat in which the pipette tips are held. For example, U.S. Pat. No. 5,324,482 to Scaramella et al. describes a pipette tip packaging system wherein a transfer plate is used to pick up flats of pipette tips by engaging a latching mechanism on the transfer plate with a latching aperture in the pipette tip flat.
A disadvantage of the first method is that it cannot be used to transport pipette tips when they are not stored within a rack or flat. The ability to transport pipette tips apart from racks or flats is desirable in many applications. For example, pipette tips are typically sold packaged in flats, and much existing equipment is designed to process racks, rather than flats, of pipette tips. The first method cannot be used to remove pipette tips from the flat in which they are packaged and set them into a rack for processing, or conversely, to remove pipette tips from the rack after processing and return them to the flat.
In the second method used by the industry to transport pipette tips, the tips are frictionally engaged by a device which then moves the tips. Usually the pipette tips must be force-fit onto some structure to achieve the frictional engagement. This method has typically been used in devices which are primarily designed to draw and expel liquid into and from the pipette tips while they are engaged upon the device. The frictional engagement of the pipette tips is necessary to hold the pipette tips in position while suction is applied to draw the liquid into the pipette tip or suction is released to expel liquid from the pipette tip.
For example, U.S. Pat. No. 5,063,790 to Freeman et al. and U.S. Pat. No. 5,736,105 to Astle each describe an apparatus which comprises one or more structures (nozzles, in Freeman et al., or pin extensions, in Astle) onto each of which a pipette tip may be fitted and sealed. The inner surface of the pipette tip head is frictionally engaged by one or more O-rings fitted upon the structure. While the pipette tips are engaged, each apparatus may be used to carry out a liquid handling task.
The frictional engagement of the pipette tips causes stress to the pipette tips which can distort the shape of the tips or otherwise cause them damage. Further, frictional engagement necessarily requires substantial contact between each pipette tip and the structure to which the pipette tip is attached, increasing the risk that a pipette tip will become contaminated by the apparatus or that the apparatus will become contaminated by the pipette tip.
Further, because these apparatus engage the pipette tips by friction, the apparatus must utilize additional structures to push the pipette tips off of the apparatus. This causes additional wear and tear on the pipette tips. Uneven application of the pressure to release the pipette tips may also cause the pipette tips to become misaligned when pushed off into a supporting structure such as a rack or flat.
Accordingly, the primary object of the present invention is to provide an apparatus which can transport pipette tips independently of racks or flats without frictionally engaging the pipette tips.
Other objects and advantages of the current invention will become apparent when the inventive apparatus for transporting pipette tips is considered in conjunction with the accompanying drawings, specification, and claims.